Selective Small-molecule Kinase Inhibitors Research Articles

Abstract 4029: HPK1 inhibitor reinvigorates exhausted tumor-infiltrating CD8 T cells and synergizes with anti-PD-1 blockade in gynecologic malignancies

Abstract HPK1 (Hematopoietic Progenitor Kinase 1) is a negative intracellular immune checkpoint that interferes with the priming and activation of T cells. In recent years, several HPK1 inhibitors have been discovered as novel immune-oncology drugs with promising potential to improve anti-tumor immune responses. However, there has been no study showing the effects and potential application of HPK1 in gynecologic malignancies. Therefore, we investigated the expression and role of HPK1 in tumor-infiltrating CD8 T cells (CD8 TILs) and how the selective small molecule kinase inhibitor, FB849, affected the reinvigoration of exhausted CD8 TILs in gynecologic cancers. We isolated TILs from patients with newly diagnosed endometrial (n=53) and ovarian cancer (n=46). The immunological properties and HPK1 signaling pathway of CD8 TILs were explored using flow cytometry. TILs were in vitro stimulated with anti-CD3 in the presence of FB849 and/or anti-PD-1, and their proliferation was assessed. We observed that HPK1 marked severely exhausted PD-1+CD8 TILs, and high HPK1 expressers had more exhausted PD-1+CD8 TILs compared to low HPK1 expressers. In addition, FB849 could successfully restore the effector function of exhausted CD8 TILs. In particular, the reinvigorating capacity of FB849 was negatively correlated with phosphorylated SLP76+PD-1+CD8 TILs in endometrial cancer. In addition, FB849 further enhanced anti-PD-1-mediated reinvigoration of CD8 TILs in endometrial cancer. However, there was no synergistic effect of FB849 + anti-PD-1 in terms of proliferative capacity in ovarian cancer. Overall, the results of our present study provide a rationale for clinical trials investigating the anti-tumor efficacy of FB849 ± anti-PD-1 tailored to the respective properties of gynecologic malignancies. Citation Format: Junsik Park, Yong Jae Lee, Sunghoon Kim, Seungmook Lim, A Yeong Park, Jamie Jae Eun Kim, Jinhwa Lee, Sang Wun Kim, Su-Hyung Park, Jung-Yun Lee. HPK1 inhibitor reinvigorates exhausted tumor-infiltrating CD8 T cells and synergizes with anti-PD-1 blockade in gynecologic malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4029.

Acetylation of the Catalytic Lysine Inhibits Kinase Activity in PI3Kδ

Covalent inhibition is a powerful strategy to develop potent and selective small molecule kinase inhibitors. Targeting the conserved catalytic lysine is an attractive method for selective kinase inactivation. We have developed novel, selective inhibitors of phosphoinositide 3-kinase δ (PI3Kδ) which acylate the catalytic lysine, Lys779, using activated esters as the reactive electrophiles. The acylating agents were prepared by adding the activated ester motif to a known selective dihydroisobenzofuran PI3Kδ inhibitor. Three esters were designed, including an acetate ester which was the smallest lysine modification evaluated in this work. Covalent binding to the enzyme was characterized by intact protein mass spectrometry of the PI3Kδ-ester adducts. An enzymatic digest coupled with tandem mass spectrometry identified Lys779 as the covalent binding site, and a biochemical activity assay confirmed that PI3Kδ inhibition was a direct result of covalent lysine acylation. These results indicate that a simple chemical modification such as lysine acetylation is sufficient to inhibit kinase activity. The selectivity of the compounds was evaluated against lipid kinases in cell lysates using a chemoproteomic binding assay. Due to the conserved nature of the catalytic lysine across the kinome, we believe the covalent inhibition strategy presented here could be applicable to a broad range of clinically relevant targets.

Bone morphogenetic protein receptors: Structure, function and targeting by selective small molecule kinase inhibitors.

Bone morphogenetic proteins (BMPs) are secreted cytokines that control the fate and function of many different cell types. They exert their cellular responses via heteromeric complexes of specific BMP type I and type II serine/threonine kinase receptors, e.g. BMPRIA and BMPRII. Three type II and four type I receptors, also termed activin receptor-like kinases (ALKs), have been identified. The constitutively active type II kinase phosphorylates the type I receptor, which upon activation initiates intracellular signaling by phosphorylating SMAD effectors. Auxiliary cell surface receptors without intrinsic enzymatic motifs, such as Endoglin and Repulsive guidance molecules (RGM), can fine-tune signaling by regulating the interaction of the BMP ligands with the BMPRs. The functional annotation of the BMPR encoding genes has helped to understand underlying mechanisms of diseases in which these genes are mutated. Loss of function mutations in BMPRII, Endoglin or RGMc are causally linked to pulmonary arterial hypertension, hereditary hemorrhagic telangiectasia and juvenile hemochromatosis, respectively. In contrast, gain of function mutations in ACVR1, encoding ALK2, are linked to Fibrodysplasia ossificans progressiva and diffuse intrinsic pontine glioma. Here, we discuss BMPR identification, structure and function in health and disease. Moreover, we highlight the therapeutic promise of small chemical compounds that act as selective BMPR kinase inhibitors to normalize overactive BMPR signaling.

Abstract LB-368: Determining and characterizing differential biodistribution of tumor derived exosomes by non-invasive nuclear imaging

Abstract Introduction: New theory of “seeds (cancer cells) and soil (distant tissue)” transpired as scientists acquainted exosomes as seeds that cruise to distant organs and release growth factors (fertilizers) to acclimate the “foreign soil” and prepare the metastatic niche. Exosomes are nano-sized (30-150nm) spherical organelles, derived from the endosomal system for intercellular communications. Tumor derived exosomes (TDEs) play an imperative role in tumor growth, stromal reorganization, cancer stemness, neovascularization, and metastatic niche formation by providing proteins, lipids, mRNA, miRNA etc. to tumor microenvironment. Despite intense research in the field, only few studies have investigated exosome biodistribution and thus very little known about their in vivo trafficking, that is also impeding their biomedical application as diagnostic and prognostic marker and as a potential therapeutic delivery vehicle. Also, it would be of interest to investigate the biodistribution of exosomes isolated from tumor cells after different treatment. Application of nuclear imaging techniques, such as single-photon emission computed tomography (SPECT) using radio isotopically labeled exosomes have indisputable advantages over fluorescent imaging regarding tissue penetration and quantitative measurement of the biodistribution. Methods: To determine in vivo trafficking of TDEs and whether exosomes from treated cells are distributed differently, we isolated exosomes from hypoxic (1% O2) 4T1 breast cancer cells without any treatment (control), and treated with GW2580 or HET0016 drug. GW2580, a selective small molecule kinase inhibitor of colony stimulating factor 1-receptor (CSF-1R) and HET0016 that is a highly selective inhibitor of CYP4A in arachidonic acid pathway, have been shown to decrease tumor growth and metastasis. We labeled these three groups of exosomes with radio I-131 and injected them in 4T1 tumor bearing and non-tumor bearing Balb/c mice. Then, we followed up the radio I-131labeled exosome distribution for 3 consecutive days with SPECT. Results: More exosomes were localized in the lungs in tumor bearing mice compared to non-tumor bearing mice. Interestingly, control exosomes were more localized in the metastatic site that is in the lungs than the primary breast tumor. We observed TDEs from untreated cells were localized more in metastatic site than that exosomes from the GW2580 and HET0016 treated cells. Conclusion: This study demonstrates that treatment of tumor cells with drugs that inhibit tumor growth and metastasis potentially yield exosomes with less protumorigenic and less metastatic characteristics and become less homing to metastatic site. TDEs are more efficiently visualized and quantified in vivo by radio-isotope labelling of exosomes. The knowledge attained from this study will open up new horizon in exosome research and biological nanotechnology for diagnosis and prognosis and targeted treatment. Citation Format: Mohammad Harun Rashid, Thaiz Borin, Kartik Angara, Roxan Ara, Achyut Bhagelu, Ali Arbab. Determining and characterizing differential biodistribution of tumor derived exosomes by non-invasive nuclear imaging [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-368.

Abstract LB-B15: A novel PI3K gamma isoform selective small molecule kinase inhibitor demonstrates single agent anti-tumor activity and enhanced combination activity with checkpoint blockade in syngeneic mouse models of cancer

Abstract Immune checkpoint inhibitors have generated impressive clinical responses, however, a number of patients and cancer types remain resistant to checkpoint blockade. Immunosuppressive cells such as Tregs and MDSCs in the tumor microenvironment are hypothesized to mediate this resistance. The gamma (γ) isoform of PI3K has long been known to modulate myeloid and lymphocyte cell migration and function, including trafficking of monocytic and granulocytic cells into inflamed tissues such as tumors. Here we report the identification and characterization of BVD-723, a PI3Kγ selective small molecule kinase inhibitor which demonstrated single agent and enhanced combination anti-tumor activity[xx]with either an anti-PD-1 or anti-CTLA-4 antibody. In a mouse syngeneic colon cancer model,[xx]BVD-723 in combination with anti-PD-1 or anti-CTLA-4 resulted in complete regression[xx]of tumors in 35% (7/20) and 60% (12/20) of animals treated with each antibody respectively [versus 0% (0/20) and 5% (1/20) with either antibody alone]. Interestingly, the anti-tumor activity was coupled with a decrease in tumor infiltrating Tregs, granulocytic MDSCs, CD4+ T cells and an increase in the CD8+/Treg ratio, suggesting that inhibition of PI3Kγ by BVD-723 promotes immune-reactivation in the tumor microenvironment. Additionally, BVD-723 demonstrated potent synergy with an anti-PD-1 antibody in a syngeneic mouse model of lymphoma. Single agent BVD-723 activity was also observed in syngeneic mouse models of pancreas, colon, lymphoma and bladder cancers. Results from completed safety pharmacology, toxicology and in vivo efficacy studies support clinical evaluation of BVD-723[xx]as a monotherapy or in combination with the checkpoint inhibitors in cancer.[xx] Citation Format: Saurabh Saha, Linping Zhang, Thomas Hoock, Alex Aronov, Sudipta Mahajan, Michael Boyd, Jon Come, Veronique Damagnez, Wojciech Dworakowski, Suvarna Khare-Pandit, Arnaud LeTiran, Cameron Moody, Harwin O'Dowd, Joseph Prezioso, Setu Roday, Xiaoyan M. Zhang. A novel PI3K gamma isoform selective small molecule kinase inhibitor demonstrates single agent anti-tumor activity and enhanced combination activity with checkpoint blockade in syngeneic mouse models of cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr LB-B15.

Exploring the Complex Universe of Fixed-Income ETFs: Is More Better or Is Less More?

Vascular endothelial growth factor (VEGF) is a key driver of the neovascularization and vascular permeability that leads to the loss of visual acuity in diabetic retinopathy and neovascular age-related macular degeneration. Our aim was to identify an orally active, selective small molecule kinase inhibitor of vascular endothelial growth factor receptor (VEGFR)-2 with activity against both VEGF-induced angiogenesis and vascular permeability. We used a biochemical assay to identify 3-[5-methyl-2- (2-oxo-1,2-dihydro-indol-3-ylidenemethyl)-1<i>H</i>-pyrrol-3-yl]-proprionic acid (SU10944), a pyrrole indolinone, which is a potent ATP-competitive inhibitor of VEGFR-2 (<i>K</i>_i of 21 ± 5 nM). In cellular assays, SU10944 inhibited VEGF-induced receptor autophosphorylation (IC₅₀ of 227 ± 80 nM) as well as downstream signaling (IC₅₀ of 102 ± 27 nM). In biochemical assays, SU10944 exhibits potent inhibitory activity against VEGFR-1; weak activity against other related subgroup members, including stem cell factor receptor (SCFR), platelet-derived growth factor receptor β (PDGFRβ), and fibroblast growth factor receptor-1 (FGFR-1); and no detectable activity against other protein tyrosine kinases such as epidermal growth factor receptor (EGFR), Src, and hepatocyte growth factor receptor. In cellular assays, the selectivity for SU10944 to inhibit VEGFR is maintained compared with other tyrosine kinases (IC₅₀ for SCFR of 1.6 ± 0.3 μM, for PDGFRβ of 30.6 ± 13.3 μM, for FGFR-1 of &gt;50 μM, and for EGFR of &gt;50 μM). Upon oral administration, SU10944 gave a clear dose response in the corneal micropocket model with an ED₅₀ value for inhibition of neovascularization of ∼30 mg/kg and a maximum inhibition of 95% at 300 mg/kg. Similarly, upon oral administration in the Miles assay, SU10944 potently inhibited VEGF-induced vascular permeability. Our data indicate that small molecule inhibitors of VEGFR signaling have the potential to ameliorate VEGF-induced neovascularization as well as vascular permeability.

Abstract 1827: Inhibition of Src, HER2, and EGFR by the multi-kinase inhibitor KD019 overcomes trastuzumab resistance in breast cancer

Abstract KD019 (previously EXEL-7647) is an orally bioavailable spectrum selective small molecule kinase inhibitor of Src family nonreceptor tyrosine kinases (Src) as well as HER2, EGFR, and VEGFR2/KDR. Because of its complement of targets KD019 is able to disrupt multiple components of tumor pathology and, in earlier studies, KD019 demonstrated robust activity in multiple in vivo tumor models. In recent years Src has emerged as a critical convergent node downstream of multiple signaling cascades initiated by transmembrane receptor tyrosine kinases (RTKs), most notably HER2, EGFR and IGF-1R. Crosstalk between Src and RTKs facilitates RTK-dependent tumor growth and, in patients with HER2-amplified (HER2+) breast cancer, where Src is upregulated, may confer resistance to anti-HER2 therapies. Based on the target specificity of KD019, including Src, we hypothesized that KD019 may prove to be an effective treatment in overcoming trastuzumab resistance in HER2+ breast cancer. Here we present data showing that KD019 effectively inhibited growth of several trastuzumab resistant cell lines with IC50 of 0.3 uM in vitro. Not only did KD019 potently inhibit HER2 and EGFR phosphorylation in these cells, but it also efficiently inhibited the phosphorylation of c-Met through receptor hetero-oligomerization mechanism, thus downregulating another pathway by which tumors may escape HER2 targeted therapies. Further, we demonstrate that once daily dosing of KD019 strongly inhibited tumor growth in xenograft models of trastuzumab resistance and that Src activity was inhibited in KD019 treated tumors even 24 hrs after drug administration. The significance of inhibiting the specific combination of targets is underscored by the fact that KD019 was 10 fold more potent when compared to saracatinib (a selective Src inhibitor) in inhibiting growth of trastuzumab resistant cells, which are also insensitive to blockade of individual RTKs. Together, these results provide a rational for clinical investigation of KD019 in patients whose tumors are resistant to anti-HER2 therapies. Citation Format: Rigen Mo, Nishta Rao, James Tonra, Samuel Waksal, Masha Poyurovsky. Inhibition of Src, HER2, and EGFR by the multi-kinase inhibitor KD019 overcomes trastuzumab resistance in breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1827. doi:10.1158/1538-7445.AM2014-1827

466P - Targeting Resistance in Egfr-Mutant Non-Small Cell Lung Cancer (Nsclc): Preclinical Evidence Supporting the Combination of Egfr Tyrosine Kinase Inhibitors (Tkis) Azd9291 and Gefitinib with Molecularly Targeted Agents and Immunotherapeutics

ABSTRACT Aim: First-generation EGFR-TKIs, such as gefitinib, are active in first-line, EGFR-TKI-sensitising-mutant (EGFRm+), advanced NSCLC, but the duration of clinical benefit is limited by acquired tumour resistance. A common resistance mechanism is gain of an additional mutation, T790M, and about 5–15% of patients also develop MET amplification, with or without T790M. The recently developed novel third-generation EGFR-TKI, AZD9291 (a selective EGFR-TKI of EGFRm+ and T790M mutations), overcomes T790M-mediated resistance. Combining EGFR-TKIs with selective molecularly targeted agents has the potential to delay the emergence of EGFR-TKI resistance across lines of therapy. Finally, immunotherapeutics, such as checkpoint inhibitors, have the potential to target cancers orthogonally; thus studies to optimise their use with EGFR-TKIs would be of high value to patients. Methods: In vitro and in vivo preclinical models representing EGFRm+ and T790M NSCLC were used to investigate the potential of combining AZD9291 or gefitinib with immunotherapeutics, and selective small molecule kinase inhibitors, namely selumetinib (AZD6244, ARRY-142886; MEK1/2 inhibitor) and AZD6094 (MET inhibitor). Results: Preclinical models harbouring MET overexpression demonstrated AZD6094 plus EGFR-TKI was well tolerated and effective in reversing MET-driven resistance. In models of acquired resistance mediated by increased MEK dependency, resistance could be delayed in vitro and in vivo by addition of selumetinib. Finally, a genetically engineered mouse model of mutant EGFR NSCLC was used to assess the impact of AZD9291 treatment on T-cell infiltration; results will be presented. Conclusions: These preclinical studies provide a strong rationale for the clinical evaluation of AZD9291 and gefitinib in combination with molecularly targeted agents, such as AZD6094 and selumetinib, to delay and/or overcome acquired resistance to single-agent EGFR-TKI therapy. Rational combinations with immunotherapeutics are also worth further investigation. Disclosure: D. Cross, C. Eberlein, S. Ashton, M. Mellor, P. Smith, M. Frigault and P.J. Jewsbury: Employment and stock ownership: AstraZeneca; C. D'Cruz: Employment: AstraZeneca; R. Stewart: Employment: MedImmune. Stock ownership: AstraZeneca; A. Schuller: Employment: AstraZeneca; W. Pao: Rights to EGFR T790M testing licensed on WP's behalf by MSKCC to MolecularMD. Research funding and travel and consulting funds: AstraZeneca. All other authors have declared no conflicts of interest.

Detection of Allosteric Kinase Inhibitors by Displacement of Active Site Probes

Non–adenosine triphosphate (ATP) competitive, allosteric inhibitors provide a promising avenue to develop highly selective small-molecule kinase inhibitors. Although this class of compounds is growing, detection of such inhibitors can be challenging as standard kinase activity assays preferentially detect compounds that bind to active kinases in an ATP competitive manner. We have previously described a time-resolved fluorescence resonance energy transfer (TR-FRET)–based kinase binding assay using the competitive displacement of ATP competitive active site fluorescent probes (“tracers”). Although this format has gained acceptance, published data with this and related formats are almost entirely without examples of non-ATP competitive compounds. Thus, this study addresses whether this format is useful for non-ATP competitive inhibitors. To this end, 15 commercially available non-ATP competitive inhibitors were tested for their ability to displace ATP competitive probes. Despite the diversity of both compound structures and their respective targets, 14 of the 15 compounds displaced the tracers with IC50 values comparable to literature values. We conclude that such binding assays are well suited for the study of non-ATP competitive inhibitors. In addition, we demonstrate that allosteric inhibitors of BCR-Abl and MEK bind preferentially to the nonphosphorylated (i.e., inactive) form of the kinase, indicating that binding assays may be a preferred format in some cases.

Molecularly Targeted Therapy: Great Progress or Evil Cycle

Therapeutic mode of cancer patients have shifted during a past few decades from the administration of broadly effective conventional anticancer agents towards the more-specific therapies in individual case and each cancer. This strategy derived from the notion that cancer cells usually become more dependent on and addicted to the activity of a specific molecule which in most cases, is an oncogene product. Along with the prevalence of this concept “oncogene addiction”, this novel and specific therapy called “tailored targeted therapy” came true for each patient [1,2]. The rationale of targeting the molecule selectively overexpressed or activated in cancer cells is that cytotoxicity will be selective/specific for cancer cells, minimizing potential adverse events (AEs). Therefore, effective tailored targeted therapy requires the initial and essential effort to identify the key molecule(s) by which downstream pathways are activated. The representative target molecule has been protein kinase, and thus, receptor tyrosine kinases and the downstream effectors (phosphoinositide-3 kinases [PI3-K], Ras and Raf, etc.) have been attractive therapeutic targets. The highly conserved ATP–binding site within the catalytic domain of most kinases was initially viewed as an appropriate target for the development of selective small-molecule kinase inhibitors. Later, the non-ATP-competitive kinase inhibitors were found to show the higher selectivity without affecting other protein kinases. Eventually, this trial spurred the development of more than 500 molecularly targeted pharmacological agents and about 150 kinase-targeted drugs, and ushered in an era of “molecularly targeted therapy” (MTT) [3].

A novel Aurora kinase A inhibitor MK-8745 predicts TPX2 as a therapeutic biomarker in non-Hodgkin lymphoma cell lines

Selective small-molecule kinase inhibitors have encouraging clinical efficacy in several malignancies. These agents are still limited to a subset of patients, indicating the need to develop therapeutic biomarkers that influence clinical benefit. In this study, we demonstrate that treatment with MK-8745, a novel Aurora-A specific inhibitor, leads to cell cycle arrest at the G2/M phase with accumulation of tetraploid nuclei followed by cell death in non-Hodgkin lymphoma (NHL) cell lines. The sensitivity of the cell lines to MK-8745 is correlated with the expression level of Aurora-A activator. The siRNA knockdown of Aurora-A activator TPX2 (targeting protein for Xenopus kinase-like protein 2) increased MK-8745 sensitivity in less-MK-8745-sensitive NHL cell lines, whereas overexpression of TPX2 in high-MK-8745-sensitive NHL cell lines increased drug resistance. Our results indicate that TPX2 may serve as a biomarker for identifying subpopulations of patients sensitive to Aurora-A inhibitor treatment.

Abstract 4501: INK1117: A potent and orally efficacious PI3Kα-selective inhibitor for the treatment of cancer

Abstract Objective: Discovery, characterization and preclinical evaluation of PI3Kalpha (PI3Kα) selective small molecule kinase inhibitors for the treatment of solid tumors. Background: The PI3K pathway is one of the most frequently dysregulated pathways in human cancer. Activating mutations in the PIK3CA gene, encoding the p110 catalytic subunit of PI3Kα, have been identified as a major mechanism of inducing oncogenic PI3K signaling. The high frequency of PIK3CA mutations suggests that PI3Kα inhibitors may have therapeutic utility in genetically defined tumor populations. The discovery of isoform-selective PI3Kα inhibitors has proven to be difficult due to the highly homologous nature of all PI3K isoforms and structurally related kinases. Multiple non-selective class I PI3K (pan-PI3K) inhibitors have entered clinical development. PI3Kα-selective inhibitors may permit more potent inhibition of PI3Kα while minimizing side effects and permitting more alternatives for combination therapy relative to pan-PI3K pathway inhibitors. Results: Through structure-guided drug design we have discovered INK1117, a novel, potent and selective PI3Kα inhibitor with good oral bioavailability. INK1117 potently inhibits PI3Kα and demonstrates a greater than 100-fold selectivity relative to other class I PI3K family members and mTOR as well as a high degree of selectivity against a large panel of protein kinases. INK1117 blocks proliferation of tumor cell lines bearing PIK3CA mutations, and inhibits cellular phosphorylation and activity of AKT. However, INK1117 shows much less activity in PTEN-deficient tumor cells, which typically display constitutive PI3K pathway activation independent of PI3Kα. INK1117 blocks VEGF signaling and angiogenesis in vitro and in vivo. Daily, oral administration of INK1117 potently inhibits tumor growth in xenograft models bearing PIK3CA oncogenic mutations and, comparable to in vitro studies, INK1117 was not efficacious in tumor models with PTEN and/or KRAS mutations. In contrast to pan-PI3K inhibitors, INK1117 does not appear to impair glucose homeostasis or insulin response in glucose/insulin tolerance tests in rodents. Additionally, INK1117 does not significantly impair B and T cell function in vitro and in vivo. These two factors support the hypothesis that INK1117 may be better tolerated than pan-PI3K inhibitors, particularly when used in combination with other agents. Conclusion: INK1117 is a potent and orally efficacious PI3Kα isoform-selective kinase inhibitor with excellent drug-like properties. Selectively targeting PI3Kα offers a new therapeutic approach for the treatment of cancers with PIK3CA activation and preclinical data suggest that isoform-selective inhibitors may provide equivalent efficacy to pan-PI3K inhibitors in selected tumors with a more favorable safety profile. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4501. doi:10.1158/1538-7445.AM2011-4501

Modeling Bone Marrow Toxicity Using Kinase Structural Motifs and the Inhibition Profiles of Small Molecular Kinase Inhibitors

The cellular function of kinases combined with the difficulty of designing selective small molecule kinase inhibitors (SMKIs) poses a challenge for drug development. The late-stage attrition of SMKIs could be lessened by integrating safety information of kinases into the lead optimization stage of drug development. Herein, a mathematical model to predict bone marrow toxicity (BMT) is presented which enables the rational design of SMKIs away from this safety liability. A specific example highlights how this model identifies critical structural modifications to avoid BMT. The model was built using a novel algorithm, which selects 19 representative kinases from a panel of 277 based upon their ATP-binding pocket sequences and ability to predict BMT in vivo for 48 SMKIs. A support vector machine classifier was trained on the selected kinases and accurately predicts BMT with 74% accuracy. The model provides an efficient method for understanding SMKI-induced in vivo BMT earlier in drug discovery.

Cdk1 Activity Is Required for Mitotic Activation of Aurora A during G2/M Transition of Human Cells

In mammalian cells entry into and progression through mitosis are regulated by multiple mitotic kinases. How mitotic kinases interact with each other and coordinately regulate mitosis remains to be fully understood. Here we employed a chemical biology approach using selective small molecule kinase inhibitors to dissect the relationship between Cdk1 and Aurora A kinases during G(2)/M transition. We find that activation of Aurora A first occurs at centrosomes at late G(2) and is required for centrosome separation independently of Cdk1 activity. Upon entry into mitosis, Aurora A then becomes fully activated downstream of Cdk1 activation. Inactivation of Aurora A or Plk1 individually during a synchronized cell cycle shows no significant effect on Cdk1 activation and entry into mitosis. However, simultaneous inactivation of both Aurora A and Plk1 markedly delays Cdk1 activation and entry into mitosis, suggesting that Aurora A and Plk1 have redundant functions in the feedback activation of Cdk1. Together, our data suggest that Cdk1, Aurora A, and Plk1 mitotic kinases participate in a feedback activation loop and that activation of Cdk1 initiates the feedback loop activity, leading to rapid and timely entry into mitosis in human cells. In addition, live cell imaging reveals that the nuclear cycle of cells becomes uncoupled from cytokinesis upon inactivation of both Aurora A and Aurora B kinases and continues to oscillate in a Cdk1-dependent manner in the absence of cytokinesis, resulting in multinucleated, polyploidy cells.

Factors underlying sensitivity of cancers to small-molecule kinase inhibitors

Selective small-molecule kinase inhibitors have emerged over the past decade as an important class of anti-cancer agents, and have demonstrated impressive clinical efficacy in several different diseases, including relatively common malignancies such as breast and lung cancer. However, clinical benefit is typically limited to a fraction of treated patients. Genomic features of individual tumours contribute significantly to such clinical responses, and these seem to vary tremendously across patients. Additional factors, including pharmacogenomics, the tumour microenvironment and rapidly acquired drug resistance, also contribute to the clinical sensitivity of various cancers, and should be considered and applied in the development and use of new kinase inhibitors.

A selective and oral small molecule inhibitor of vascular epithelial growth factor receptor (VEGFR)-2 and VEGFR-1 inhibits neovascularization and vascular permeability.

Vascular endothelial growth factor (VEGF) is a key driver of the neovascularization and vascular permeability that leads to the loss of visual acuity in diabetic retinopathy and neovascular age-related macular degeneration. Our aim was to identify an orally active, selective small molecule kinase inhibitor of vascular endothelial growth factor receptor (VEGFR)-2 with activity against both VEGF-induced angiogenesis and vascular permeability. We used a biochemical assay to identify 3-[5-methyl-2- (2-oxo-1,2-dihydro-indol-3-ylidenemethyl)-1H-pyrrol-3-yl]-proprionic acid (SU10944), a pyrrole indolinone, which is a potent ATP-competitive inhibitor of VEGFR-2 (Ki of 21 +/- 5 nM). In cellular assays, SU10944 inhibited VEGF-induced receptor autophosphorylation (IC50 of 227 +/- 80 nM) as well as downstream signaling (IC50 of 102 +/- 27 nM). In biochemical assays, SU10944 exhibits potent inhibitory activity against VEGFR-1; weak activity against other related subgroup members, including stem cell factor receptor (SCFR), platelet-derived growth factor receptor beta (PDGFRbeta), and fibroblast growth factor receptor-1 (FGFR-1); and no detectable activity against other protein tyrosine kinases such as epidermal growth factor receptor (EGFR), Src, and hepatocyte growth factor receptor. In cellular assays, the selectivity for SU10944 to inhibit VEGFR is maintained compared with other tyrosine kinases (IC50 for SCFR of 1.6 +/- 0.3 microM, for PDGFRbeta of 30.6 +/- 13.3 microM, for FGFR-1 of >50 microM, and for EGFR of >50 microM). Upon oral administration, SU10944 gave a clear dose response in the corneal micropocket model with an ED50 value for inhibition of neovascularization of approximately 30 mg/kg and a maximum inhibition of 95% at 300 mg/kg. Similarly, upon oral administration in the Miles assay, SU10944 potently inhibited VEGF-induced vascular permeability. Our data indicate that small molecule inhibitors of VEGFR signaling have the potential to ameliorate VEGF-induced neovascularization as well as vascular permeability.